Investigate integrating tx signing with the gas handling antehandler changes

[natebeauregard]

https://github.com/polymerdao/monomer/pull/123 introduced a way for the monomer adapters to optionally produce signed transactions. However, this requires passing application specific context into monomer and generating a monomer specific private key to sign with.

As we gain more context on working with a custom antehandler/decorator for bypassing the deposit tx gas in https://github.com/polymerdao/monomer/issues/107, we should also investigate if bypassing tx signing could be included as well as.

If the investigation doesn't lead us to bypassing signing for deposit txs in the antehandler, we should instead look into only passing through specific parts of the app context that are relevant and should add unit tests for verifying the monomer tx signer behavior.

[natebeauregard]

@joshklop Created this issue based on our conversation during the daily meeting, feel free to elaborate on anything in here